How do 3- and 5-year-olds respond to under- and over-informative utterances?

As children learn their native languages, they come to have detailed expectations about how to refer to things. These expectations and the detection of their violations are key to inference-making processes. But what do children do when their expectations are not met? Using reaction-time measures and gaze-direction monitoring in a referential communication task, we investigated whether 3- and 5-year-olds notice the infelicity of under- and over-informative utterances and then seek out further information in order to recover the speaker's intended meaning. We tested how children resolve under-informative instructions such as "Find the orange" when there is more than one orange in view. We also tested whether instructions such as "Find the cat with a tail", in a context where there is only one, normal-looking cat, would lead them to question why the speaker was over-informative and to seek out further information. Both age groups were sensitive to the ambiguous instructions. Only 5-year-olds were significantly delayed and more likely to check their interlocutor's gaze when responding to over-informative expressions. We discuss how children's spontaneous motivation to resolve violations of expectation, coupled with increased speed of linguistic processing, drives language learning.